1. Field of the Invention
The present invention relates to an image pickup apparatus and, more particularly, to an image pickup apparatus suitable for an image pickup section of a video recording apparatus integrated with a camera, or a still video recording system.
2. Related Background Art
A video camera has a narrow dynamic range as compared to a silver chloride photographing system. In a back-light state, overexposure and underexposure states (wherein brightness levels are considerably high and low) occur, a diaphragm must be manually adjusted in a conventional video camera, or light-amount correction by stopping down the diaphragm by 1 to 2 steps is often performed in a camera having a back-light correction function
However, even if back-light correction is appropriately performed and a main object to be photographed is photographed with an appropriate exposure, an overexposure (or underexposure) occurs on its background, and the entire frame tends to become an image with only a whitish background. In this manner, the narrow dynamic range problem is left unsolved.
In an image pickup apparatus using an image pickup element such as a CCD image sensor, color separation is performed by color filters (e.g., R, G, and B) arranged in front of the element, and luminance (Y) signals and color (C) signals are formed from charges stored in photoelectric converters corresponding to the colors.
FIGS. 1A and 1B are views showing the relationship between a charge storage time and a stored charge amount of the image pickup element. A storage time required for forming an NTSC signal is about 1/60 sec. When the luminance level of an object to be photographed (including a background) is low, as shown in FIG. 1A, stored charge amounts corresponding to R, G, and B are balanced, and colors of respective portions can be well reproduced. However, when the luminance level of the object is high, as shown in FIG. 1B, one of R, G, and B is saturated (B is saturated in FIG. 1B), and as a result, a false color is reproduced.
As a conventional method of solving this problem, the following processing method is generally known. A high-level portion of the Y signal is detected, and the color signal of the detected portion is suppressed. In this conventional processing method, however, when the Y signal exceeds a given value X, no color can be reproduced. For example, a clear blue sky is reproduced in white.